Formation and properties of composites comprised of calcium-deficient hydroxyapatites and ethyl alanate polyphosphazenes

Y. E. Greish, J. L. Sturgeon, A. Singh, N. R. Krogman, A. H. Touny, S. Sethuraman, L. S. Nair, C. T. Laurencin, H. R. Allcock, P. W. Brown

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Abstract

Composites comprised of calcium-deficient hydroxyapatite (HAp) and biodegradable polyphosphazenes were formed via cement-type reactions at physiologic temperature. The composite precursors were produced by blending particulate hydroxyapatite precursors with 10 wt% polymer using a solvent/non-solvent technique. HAp precursors having calcium-to-phosphate ratios of 1.5 (CDH) and 1.6 (CDS) were used. The polymeric constituents were poly[bis(ethyl alanato)phosphazene] (PNEA) and poly[(ethyl alanato)1 (p-phenylphenoxy)1 phosphazene] (PNEA50PhPh50). The effect of incorporating the phenyl phenoxy group was evaluated as a means of increasing the mechanical properties of the composites without retarding the rates of HAp formation. Reaction kinetics and mechanistic paths were characterized by pH determination, X-ray diffraction analyses, scanning electron microscopy, and infrared spectroscopy. The mechanical properties were analyzed by compression testing. These analyses indicated that the presence of the polymers slightly reduced the rate HAp formation. However, surface hydrolysis of polymer ester groups permitted the formation of calcium salt bridges that provide a mechanism for bonding with the HAp. The compressive strengths of the composites containing PNEA50PhPh50 were superior to those containing PNEA, and were comparable to those of HAp produced in the absence of polymer. The current composites more closely match the structure of bone, and are thus strongly recommended to be used as bone cements where high loads are not expected.

Original languageEnglish (US)
Pages (from-to)3153-3160
Number of pages8
JournalJournal of Materials Science: Materials in Medicine
Volume19
Issue number9
DOIs
StatePublished - Sep 2008

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Bioengineering
  • Biomaterials
  • Biomedical Engineering

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